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है”ह”ह

IS 9844 (1981): Methods of Testing Corrosion Resistance ofElectroplated and Anodized Aluminium Coatings by NeutralSalt Spray Test [MTD 24: Corrosion Protection]

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IS 9844:1981( Reaffirmed 1999)

Indian StandardMETHODS OF TESTING CORROSION

RESISTANCE OF ELECTROPLATED ANDANODIZED ALUMINIUM COATINGS

BY NEUTRAL SALT SPRAY TEST

(Third Reprint OCTOBER 2000 )

UDC 669.718.7:620.193.272

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BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Gr 2I Sefitember 198 I

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Is: !M44-1981

( Continued from page 1 )

Members SHRI S. N. GANA

Representing Indian Posts and Telernavhs Deoartment. Calcutta

SHRI P. B. SYAM ( Ahnate ) &RI~.~IRALAL NGEF Ltd. Bangslore

Smu ASWATHANARAYANA ( Alternate ) SHRI V. S. KULKARNI Grauer and Weil ( India ) Ltd. Bombay

SE& SIJ~~L GOINKA ( Alterm&? ) DR S. K. NARAN~ National Metallurgical Laboratory ( CSIR ),

SHRI R. SEN Jamshedpur

Hindustan Cables Ltd. Rupnaralnpur ( Dist. Burdwan )

SHRI KALYAN GHOELH ( AIter~te ) SHRI R. A. SHAH Ronuk Industries Ltd, Bombay

KIJMARI MRILXILA A. SHAH ( Alternote ) SHRI R. S~MASBKHARA Bharat Electronics Ltd, Bangalore

SHRI K. NAOE~H ( Alternute ) Smu V. THIYA~A~AN Development Commissioner ( Small Industries

Servicea Institute ), New Delhi SHIU R. VENKATARAMAN T. I. Qclcs of India. Madras SHRI C. R. RAMA RAO, Director Geueral, ISI ( &-o@io Menher ) Director ( Strut & Met )

Secretaries SHRI 0. N. DAXX.JPTA

Deputy Director ( Met ), IS1 SHRI S. K. GUFTA

Assistant Director ( Met ). IS1

2

Indian Standard METHODS OF TESTING CORROSION

RESISTANCE OF ELECTROPLATED AND ANODIZED ALUMINIUM COATINGS

BY NEUTRAL SALT SPRAY TEST

0. FOREWORD

0.1 This Indian Standard was adopted by the kndian SUmlards Institution on 29 May 1981, after the draft finalized by the Metallic Finishes .seCtional Committee had been approved by the Structural and w r)ivision Council.

0.2 There is seldom a direct relation between resistance to Mm of salt spray and resistance to corrosion in other media because several factors influencing the progress of corrosion, such as the formation of ps&ective films, vary greatly with the conditions encountered. Therefore, tbo dts obtained in the test should not be regarded as a direct guide to the, cerr&on resistance of the tested coatings in all environments where these .co@ngs may be used. Also, performance of different coatings in the test shouldnot be taken as a direct guide to the relative corrosion resistance of these coat- ings in service. 0.3 Anodized aluminium with coating thickness below 3 micrometres ( primarily for decorative purposes ) are not recommended for this test.

0.4 While preparing the standard, necessary assistance has been derived from IS0 3768-1976 - Metallic coatings - Neutral salt spray test ( NSS Test ), published by the International Organization for Standardization. 0.5 In reporting the result of a test or analysis made in accordance with this standard, if the final value, observed or calculated is to be rounded off, it shall be done ‘in accordance with IS : 2-1960*.

1. SCOPE

1.1 This standard specifies the apparatus, the reagent and the procedure to be used in conducting the neutral salt spray test for assessment of the quality of coatings made in accordance with the requirements of coating or product specifications.

*Rules for round@ off numerical values ( revised ).

3

IS : 9844 - 1981

1.2 It does not specify the type of test specimen, the exposure period to be used for a particular product or the interpretation of results. Such details are provided in the appropriate coating or product specifications.

2. TEST SOLUTION

2.1 The test solution shall be prepared by dissolving sodium chloride in distilled or de-ionized water to produce a concentration of 50 f 5 g/l. The sodium chloride shall be white and shall give a colourless solution in water. It shall be substantially free from copper and nickel and shall not contain more than 0.1 percent of sodium iodide and not more than O-4 percent of total impurities calculated for dry salt. .If the pH of the solution as prepared is outside the range 6.0 to 7.0, the presence of undesirable impurities in the salt or the water or both shall be investigated.

2.2 The pH of the salt solution shall be adjusted so that the pH of sprayed solution collected within the test cabinet ( see 3.1.4 ) will be between 6.5 and 7.2. Control of the pH shall be based on electrometric measurement at 25°C but a short-range pH paper which can be read in increments of 0.3 pH unit or less and ‘which has been calibrated against electrometric measurements may be used in routine checks. Any necessary correction shall be made by additions of solutions of hydrochloric acid or sodium hydroxide of analytical grade.

2.2.1 Attention is drawn to the possible changes in pH resulting from loss of carbon dioxide from the solution when it is sprayed. Such changes may be avoided by reducing the carbon dioxide content of the solution byj for example, heating it to a temperature above 35°C before it is placed in the apparatus or by making the solution from freshly boiled water.

2.3 The solution shall be filtered before it is placed in the reservoir of the ,apparatus, in order to remove any solid matter which might block the apertures of the spraying device.

3. A&ARATUS

3.1 ‘The apparatus shall comprise the following components.

3.1.1 A Spray Cabinet, made of or lined with, material resistant to corrosion by the sprayed solution. The cabinet shall have a volume of not less than 0.2 ms and preferably of not less than 0.4 m* since, with smaller volumes, difficulties are experienced in ensuring even distribution of spray. The upper parts shall be so shaped that drops of sprayed solution accumulated on them do not fall on specimens being tested.

The size and shape of the cabinet shall be such that the quantity of solution collected in the cabinet is within the limits stated in 6.2.

3.1.2 Means of Supplying and Controlling Heat - Adequate to maintain the cabinet and its contents at the specified temperature (see 6.1). The

4

IS:9844-1981

temperature shah be controhed by a thermostat element placed either within the cabinet at least 100 mm from the walls or in a water jacket on the cabinet. In either case the thermometer, capable of being read from the outside, shall be placed within the cabinet at least 100 mm from the walls.

3.1.3 Means for Spraying the Salt Solution - Comprising a supply of clean air of controlled pressure and humidity, a reservoir to contain the solution to be sprayed and one or more atomizers made of material resistant to the solution.

3.1.3.1 The compressed air supply to the atomizers shall be passed through a filter to remove all traces of oil or solid matter and shall be at a pressure of 70 to 170 kpa*. In order to prevent evaporation of water from the sprayed droplets the air shall be humidsed before entering the atomizer by passage through a saturation tower containing water at a temperature several degrees higher than that of the cabinet. The appropriate tempera- ture depends on the pressure used and on the type of atomizer nozzle and shall be adjusted so that the concentration of the collected spray are kept within the specified limits (see 6.2 ).

3.1.3.2 The reservoir to contain the solution to be sprayed shall be a tank made of material resistant to the solution and shah be provided with means of maintaining a constant level of solution in the reservoir.

3.1.3.3 The atomizers shall be made of inert material, for example, glass or plastics material. Baffles may be used to prevent direct impinge- ment of spray on the test specimens and the use of adjustable baffles is helpful in obtaining uniform distribution of spray throughout the cabinet.

3.1.4 At least two suitable collecting devices which shall be funnels of glass or other chemically inert material with the stems inserted into gradua- ted cylinders or other containers. Funnels with a diameter of 100 mm have a collecting area of approximately 80 cm%. The collecting devices shall be placed in the zone of the cabinet &here the test specimens are placed, one close to an inlet of spray and one remote from an inlet. They shall be so placed that only spray and not liquid falling from specimens or from parts of the cabinet is collected.

3.2 If the equipment has been used for a spray test or for any other purpose with solution differing from that specified for the test to be carried out, it shall be thoroughly cleaned before use.

4. TEST SPECIMENS 4.1 The number and type of test specimens, their shape and their dimensions shall be seIected according to the specification covering the coating on

‘1 kPa = 1 kN/m* - 091 a&t.

5

IS : 9844 - 1981

product being tested. When not so specified, details concerning the speci- mens shall be mutually agreed between the interested parties.

4.2 The specimens shall be thoroughly cleaned before testing. The cleaning method employed shall depend on the nature of the surface and the contaminants, and shall not include the use of any abrasives or solvents which may attack the surface of the specimens.

Care shall be taken that specimens are not recontaminated after cleaning by excessive or careless handling. 4.3 If test specimens are cut from a larger coated article, the cutting shall be carried out in such a way that the coating is not damaged in the area adjacent to the cut. Unless otherwise specified, the cut edges shall be adequately protected by coating them with a suitable medium, stable under the condi- tions of the test, such as paint, wax or adhesive tape.

5. METHOD OF EXPOSURE OF TEST SPECIMENS

5.1 The specimens shall be so placed in the cabinet that they are not in the direct line of travel of spray from the atomizer. Baflles may be used to pre- vent direct impact of the sprayed solution and the specimens.

5.2 The angle at which the sample is exposed in the cabinet is very impor- tant. The surface shall in principle, be flat and placed in the cabinet facing upwards at an angle as close as possible to 20’ to the vertical. shall, in all cases, be within the limits 15 to 30”.

This angle

In the case of irregular surfaces, for example, entire components, these limits shall be adhered to as closely as possible.

5.3 The specimens shall be so arranged that they do not come into contact with one another or with the cabinet and that surfaces to be tested are exposed to free circulation of spray. Specimens may be placed at different levels within the cabinet as long as the solution may not drip from speci- mens or their supports at one level onto other specimens placed below.

5.4 The support for the specimens shall be made of inert non-metallic material such as glass, plastics or suitably coated wood. Ifit is necessary to suspend test specimens, the material used shall on no account be metallic and shall be synthetic fibre, cotton thread or other inert insulating material.

6. OPERATING CONDITIONS

6.1 The temperature inside the spray cabinet shall be 35f2”C with the minimum possible fluctuation throughout the cabinet during the test.

6.2 The solution collected in each of the collecting devices (see 3.1.4) shall have a sodium chloride concentration of 50f 10 g/l and a pH value in the range 6.5 to 7.2 (see 2.2).

6

IS :9&4- ml

The average rate of collection of solution in each device measured over a minimum period of 24 hours shall be 1 to 2 ml/h for a horizontal collec- ting area of 80 cm’.

6.3 Test solution which has been sprayed shall not be reused.

7. DURATION OF TESTS

7.1 The period of test shall be as designated by the specification covering the coating or product being tested. When not specified, it shall be mutually agreed between the interested parties.

Recommended 480 h and 720 h.

periods of exposure are 2h, 6 h, 24 h, 48 h, 96 h, 240 h,

7.2 Spraying shall not be interrupted during the prescribed test period. The cabinet shall be opened only for brief visual inspections of the test specimens in position and for replenishing the salt solution in the reservoir if such replenishment cannot be carried out froin outside the cabinet.

7.3 If the end-point of the test depends on the appearance of the first sign of corrosion, the specimens not to be inspected frequently. For this reason such specimens shall not be tested together with other specimens requiring tests of predetermined duration.

7.4 A periodic visual examination of specimens under test for a predetermined period may be made but the surfaces under test shall not be disturbed and the period for which the cabinet is open shall be the minimum necessary to observe and record any visible changes.

8. CLEANING OF SPECIMENS AFTER TEST

8.1 At the end of the test period, remove the specimens from the cabinet. Allow the specimens to dry for half to one hour before rinsing, in order to reduce the risk of removing corrosion products. Before they are examined, carefully remove residues of the spray solution from their surfaces. A suitable method is to rinse or dip the specimens gently in clean running water at a temperature not exceeding 40°C and then to dry them immedia- tely in a stream of compressed air at a pressure not exceeding 200 kPa, at a distance of approximately 300 mm.

9. EVALUATION OF RESULTS

9.1 Many different criteria for the evaluation of the reSUlk3 Of Ihy test ‘=Y be applied to meet particular requirements, for example, change ln means, alteration revealed by micrographic examination or change iqmechamcal properties. Usually the appropriate criteria will be indicated m the spccl-

7

IS: 9844-1981

fixation for the coating or product tested. For most routine applications of the test, only the following need be considered:

a) appearance after test;

b) appearance after removing superficial corrosion products; c) the number and distribution of corrosion defects, that is, pits, cracks,

blisters, etc, these may conveniently be assessed by methods such as that described in IS : 6009-1970*; and

d) the time elapsing before the appearance of the first sign of corrosion.

10. TEST REPORT

10.1 The test report shall indicate the outcome of the test according to the criteria for evaluation of results prescribed for the test. The result obtained for each specimen tested and, when appropriate, the average result for a group of replicate test specimens shall be reported. The report may, if required, be accompanied by photographic records ,of the tested specimens.

10.2 The report shall contain information about the test procedure. This information may vary according to the purposes of the test and to the directions prescribed for it but a general list of the details likely to be required is as f0llOWS:

a) the description of the coating or product tested; b) dimensions and shape of the test specimen and the nature and area

of the surface tested; c) preparation of the test specimen, including any cleaning treatment

applied and any protection given to edges or other special areas;

4

e)

f)

s) h) j) k)

known characteristics of any coating, with an indication of the surface finish;

the number of test specimens subjected to the test representing each coating or product; the method used to clean test specimens after the test with, when appropriate, an indication of the loss in mass resulting from the cleaning operation; the angle at which the tested surfaces were inclined,

the test temperature; the duration of test; the properties of any test panels placed in the cabinet expressly to check the correctness of the operating conditions and the results obtained with them.

*Method for evaluation of results of accelerated corrosion tests.

8

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